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EVN detection of Aql X-1 in outburst

ATEL # 2317; V. Tudose (ASTRON), Z. Paragi (JIVE), J. Miller-Jones (NRAO), M. Garrett (ASTRON), R. Fender (SOTON), A. Rushton (JBO), R. Spencer (JBO)
on 29 Nov 2009; 12:21 UT
Password Certification: Valeriu Tudose (

Subjects: Radio, Binaries, Neutron Stars, Transients, Stars

The X-ray binary Aql X-1 has been in outburst in the last few weeks (ATEL #2288, #2296, #2299, #2302, #2303).

We observed the system on 2009 November 19 between 14:30-19:00 UT at 5 GHz with the European VLBI Network (EVN) using the e-VLBI technique. The participating radio telescopes were Effelsberg (1 Gbps), Medicina (896 Mbps), Onsala 25m (1 Gbps), Torun (1 Gbps), Westerbork (1 Gbps), Yebes (896 Mbps), and Cambridge (128 Mbps). The Lovell Telescope and Darnhall could not observe due to high winds.

The target was detected with a flux density of 0.40 +/- 0.05 mJy at the position: RA 19h 11m 16.0251s +/- 0.0003s; DEC +00d 35' 05.891" +/- 0.004". The naturally weighted map had a beam of 8.6 X 8.2 mas^2 at PA -48 deg and an rms noise of about 0.03 mJy/beam. The radio emission is not fully consistent with a compact emitting region: a marginally significant (at about 3 sigma level) extended component is observed towards south-east, up to 10 mas from the peak of the emission.

This is the first radio detection of Aql X-1 at milliarcsecond resolution. A previous attempt, during the outburst of 2009 March, was unsuccessful (ATEL #2000).

e-VLBI developments in Europe are supported by the EC DG-INFSO funded Communication Network Developments Project "ExPRES", Contract No.02662. The European VLBI Network is a joint facility of the European, Chinese, South African and other radio astronomy institutes funded by their national research councils.

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R. E. Rutledge , Editor
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